Backlight unit and liquid crystal display apparatus having light guiding member, prism sheet and reflection section

This application is the U.S. national phase of International Application No. PCT/JP2006/302352 filed 10 Feb. 2006, which designated the U.S. and claims priority to JP 2005-055401, filed 1 Mar. 2005, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a backlight unit and a liquid crystal display apparatus having the backlight unit.

BACKGROUND ART

A liquid crystal display apparatus performs displaying by varying the optical anisotropy of a liquid crystal layer, and thus varying the transmittance of light, in accordance with a voltage which is applied across the liquid crystal layer. Depending on the light which enters the liquid crystal layer when displaying, liquid crystal display apparatuses are generally classified into three types. The three types of liquid crystal display apparatuses are: transmission type liquid crystal display apparatuses, reflection type liquid crystal display apparatuses, and transflective type liquid crystal display apparatuses.

In a transmission type liquid crystal display apparatus, a backlight is disposed on the back face of a liquid crystal display device, and light from the backlight is transmitted through the liquid crystal display device so as to be perceived by the user. In a reflection type liquid crystal display apparatus, incident light through the front face is reflected by a liquid crystal display device so as to be perceived by the user. A transflective type liquid crystal display apparatus functions in a similar manner to either a transmission type liquid crystal display apparatus or a reflection type liquid crystal display apparatus, depending on the environment of use. Specifically, in an environment where externally-entering light is strong, a transflective type liquid crystal display apparatus functions similarly to a reflection type liquid crystal display apparatus; and in an environment where externally-entering light is weak, the backlight is activated, and the transflective type liquid crystal display apparatus functions similarly to a transmission type liquid crystal display apparatus. Alternatively, irrespective of the intensity of externally-entering light, a transflective type liquid crystal display apparatus performs displaying simultaneously in the two modes, i.e., a transmissive mode and a reflective mode.

In the following description, a transflective type liquid crystal display apparatus will be exemplified as a liquid crystal display apparatus.

In a commonly-used transflective type liquid crystal display apparatus, the efficiency of utilization of light from the backlight is not so high because reflection electrodes are provided. Therefore, in order to obtain the same luminance as that of a transmission type liquid crystal display apparatus which is similar in construction to the transflective type liquid crystal display apparatus, it is necessary to increase the light intensity of the backlight, thus resulting in a large power consumption. Moreover, if the regions in which transmission apertures for transmitting the light from the backlight are formed are increased, the efficiency of utilization of light from the backlight can be enhanced, but in this case the regions in which the reflection electrodes are formed are decreased, thus resulting in a low efficiency of utilization of external light.

Therefore, in a conventional liquid crystal display apparatus, a microlens array is provided between the liquid crystal display device and the backlight unit (Patent Document 1). In this liquid crystal display apparatus, a microlens array converges light at transmission apertures of a liquid crystal display device, whereby the efficiency of utilization of light is enhanced and thus an appropriate luminance can be obtained without increasing power consumption.

In another conventional liquid crystal display apparatus, a prism sheet having a sawteeth-shaped prism surface is provided on a backlight unit (Patent Document 2).

<figref idrefs="DRAWINGS">FIG. 16(</figref><i>a</i>) is a schematic cross-sectional view of a backlight unit <b>310</b> which is disclosed in Patent Document 2.

The backlight unit <b>310</b> includes: a surface light source <b>301</b> for emitting light; a prism sheet <b>304</b> for reflecting light from the surface light source <b>301</b> in the surface normal direction; and a reflector <b>305</b> which is disposed on the opposite side of the surface light source <b>301</b> from the prism sheet <b>304</b>.

The surface light source <b>301</b> includes: a light source <b>302</b> for emitting light; a reflection member <b>302</b><i>a </i>provided so as to surround the light source <b>302</b>; and a light guiding member <b>303</b> for receiving the light emitted from the light source <b>302</b> and propagating the received light. The reflection member <b>302</b><i>a </i>reflects the light emitted from the light source <b>302</b> toward the light guiding member <b>303</b>, and allows the light from the light source <b>302</b> to efficiently enter the light guiding member <b>303</b>.

The light guiding member <b>303</b> includes: a principal face (front face) <b>303</b><i>a </i>opposing the prism sheet <b>304</b>; a principal face (rear face) <b>303</b><i>b </i>opposing the reflector <b>305</b>; and an end face <b>303</b><i>c </i>which connects the front face <b>303</b><i>a </i>to the rear face <b>303</b><i>b</i>. The end face <b>303</b><i>c </i>of the light guiding member <b>303</b> receives the light emitted from the light source <b>302</b>, such that the light propagates in a propagation direction P while being repetitively reflected between the front face <b>303</b><i>a </i>and the rear face <b>303</b><i>b </i>of the light guiding member <b>303</b>. The front face <b>303</b><i>a </i>of the light guiding member <b>303</b> is parallel to the propagation direction P. As shown in <figref idrefs="DRAWINGS">FIG. 17</figref>, the rear face <b>303</b><i>b </i>of the light guiding member <b>303</b> includes regions which are tilted by a tilt angle α with respect to the propagation direction P.

<figref idrefs="DRAWINGS">FIG. 16(</figref><i>a</i>) is referred to again. The prism sheet <b>304</b> is disposed at the front face <b>303</b><i>a </i>side of the light guiding member <b>303</b>. The prism sheet <b>304</b> has a sawteeth-shaped prism surface, the prism surface having alternately-disposed prism slopes <b>304</b><i>a </i>and second prism slopes <b>304</b><i>b</i>. The prism surface of the prism sheet <b>304</b> opposes the front face <b>303</b><i>a </i>of the light guiding member <b>303</b>. Ridges <b>304</b><i>c </i>are formed at boundaries between the first prism slopes <b>304</b><i>a </i>and the second prism slopes <b>304</b><i>b</i>. In the prism sheet <b>304</b>, as shown in <figref idrefs="DRAWINGS">FIG. 18</figref>, each vertex angle between a first prism slope <b>304</b><i>a </i>and a second prism slope <b>304</b><i>b </i>is θ.

<figref idrefs="DRAWINGS">FIG. 16(</figref><i>a</i>) is referred to again. In the backlight unit <b>310</b>, light emitted from the light source <b>302</b> enters the light guiding member <b>303</b>, and propagates inside the light guiding member <b>303</b> in the propagation direction P.

As shown by the broken line of <figref idrefs="DRAWINGS">FIG. 19</figref>, when light enters an interface between the front face <b>303</b><i>a </i>of the light guiding member <b>303</b> and the air at an incident angle which is smaller than a predetermined incident angle (angle of total reflection), a portion of the light is refracted at the interface between the front face <b>303</b><i>a </i>and the air so as to be emitted forward, and a portion of the light is reflected at the interface between the front face <b>303</b><i>a </i>and the air.

On the other hand, as shown by a solid line in <figref idrefs="DRAWINGS">FIG. 19</figref>, when light enters the interface between the front face <b>303</b><i>a </i>of the light guiding member <b>303</b> and the air at an incident angle which is equal to or greater than the angle of total reflection, the light is totally reflected.

<figref idrefs="DRAWINGS">FIG. 16(</figref><i>a</i>) is referred to again. The light which has been refracted at the interface between the front face <b>303</b><i>a </i>of the light guiding member <b>303</b> and the air enters the prism sheet <b>304</b>, and is reflected in the surface normal direction by the prism sheet <b>304</b>.

Moreover, the light which has been reflected at the interface between the front face <b>303</b><i>a </i>of the light guiding member <b>303</b> and the air travels toward the rear face <b>303</b><i>b </i>of the light guiding member <b>303</b>, and the light which is refracted at the interface between the rear face <b>303</b><i>b </i>of the light guiding member <b>303</b> and the air is emitted rearward, so as to strike the reflector <b>305</b>. This light is reflected by the reflector <b>305</b>, and again enters the rear face <b>303</b><i>b </i>of the light guiding member. Thereafter, the light is emitted forward from the front face <b>303</b><i>a</i>, enters the prism sheet <b>304</b>, and is reflected by the prism sheet <b>304</b> in the surface normal direction.

Thus, in the backlight unit <b>310</b>, the light which has once been emitted from the rear face <b>303</b><i>b </i>of the light guiding member <b>303</b> is reflected by the reflector <b>305</b> so as to be used for displaying, whereby the efficiency of utilization of light from the light source <b>302</b> can be enhanced. Moreover, since the prism sheet <b>304</b> is provided in the backlight unit <b>310</b>, highly-directional light can be emitted for a liquid crystal display device (not shown). <ul><li id="ul0001-0001" num="0020">[Patent Document 1] Japanese Laid-Open Patent Publication No. 11-109417</li><li id="ul0001-0002" num="0021">[Patent Document 2] Japanese Laid-Open Patent Publication No. 11-224058</li></ul>

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

However, a sufficient luminance may not be obtained even by using a microlens array.

Moreover, when the conventional backlight unit <b>310</b> is used for a liquid crystal display apparatus, moiré fringes may occur during displaying by the liquid crystal display apparatus.

As shown in <figref idrefs="DRAWINGS">FIG. 16(</figref><i>a</i>), the light which is emitted forward from the front face <b>303</b><i>a </i>of the light guiding member <b>303</b> enters into the prism sheet <b>304</b>, and is reflected by the second prism slopes <b>304</b><i>b </i>of the prism sheet <b>304</b> so as to be emitted off the prism sheet <b>304</b> in the surface normal direction.

Moreover, the light which is emitted rearward from the rear face <b>303</b><i>b </i>of the light guiding member <b>303</b> is reflected by the reflector <b>305</b>, and becomes light having a component in a direction toward the rear face <b>303</b><i>b </i>of the light guiding member <b>303</b>, so as to again enter the light guiding member <b>303</b>. The light having entered the light guiding member <b>303</b> is finally emitted forward from the front face <b>303</b><i>a </i>of the light guiding member <b>303</b>. The light emitted forward from the front face <b>303</b><i>a </i>of the light guiding member <b>303</b> enters into the prism sheet <b>304</b>, and is reflected by the second prism slopes <b>304</b><i>b </i>of the prism sheet <b>304</b>, so as to be emitted off the prism sheet <b>304</b> in the surface normal direction.

Thus, in the conventional backlight unit <b>310</b>, both the light emitted from the light guiding member <b>303</b> without going via the reflector <b>305</b> and the light emitted from the light guiding member <b>303</b> via the reflector <b>305</b> are reflected by the second prism slopes <b>304</b><i>b </i>of the prism sheet <b>304</b>. In other words, only the second prism slopes <b>304</b><i>b </i>of the prism sheet <b>304</b> contribute to the emission of light in the surface normal direction. Therefore, the intensity of the light which is reflected by the second prism slopes <b>304</b><i>b </i>is different from the intensity of the light reflected by the first prism slopes <b>304</b><i>a. </i>

<figref idrefs="DRAWINGS">FIG. 16(</figref><i>b</i>) is a schematic diagram showing the intensity of the light emitted from the conventional backlight unit <b>310</b>. In <figref idrefs="DRAWINGS">FIG. 16(</figref><i>b</i>), out of the light emitted from the backlight unit <b>310</b>, the intensity of the light reflected by the first prism slopes <b>304</b><i>a </i>of the prism sheet <b>304</b> corresponds to reference numeral A, whereas the intensity of the light reflected by the second prism slopes <b>304</b><i>b </i>of the prism sheet <b>304</b> corresponds to reference numeral B. In the conventional backlight unit <b>310</b>, both the light traveling via the reflector <b>305</b> and the light not traveling via the reflector <b>305</b> are reflected by the second prism slopes <b>304</b><i>b </i>of the prism sheet <b>304</b>, so that the intensity of the light ascribable to the second prism slopes <b>304</b><i>b </i>(corresponding to reference numeral B) is greater than the intensity of the light ascribable to the first prism slopes <b>304</b><i>a </i>(corresponding to reference numeral A). Thus, the light which is emitted from the prism sheet <b>304</b> has bright-dark fringes corresponding to the pitch of the prism sheet <b>304</b>.

Consequently, a conventional liquid crystal display apparatus employing the backlight unit <b>310</b> performs displaying by using light which has bright-dark fringes, and therefore moiré fringes will occur during displaying by the liquid crystal display apparatus.

As a method for eliminating such moiré fringes, methods such as providing a diffusion layer for diffusing the light which is gathered at the transmission apertures of the liquid crystal display device (not shown) are known. However, providing a diffusion layer invites the problems of reduced frontal luminance and reduced displaying contrast.

An objective of the present invention is to provide a backlight unit which prevents bright-dark fringes in the emitted light, and a liquid crystal display apparatus having the backlight unit.

Means for Solving the Problems

A backlight unit according to the present invention comprises: a light source for emitting light; a light guiding member having a front face, a rear face, and an end face, the light guiding member receiving the light emitted from the light source at the end face and propagating the received light in a first direction; a prism sheet disposed at the front face side of the light guiding member; and a reflection section disposed at the rear face side of the light guiding member, wherein, the reflection section has a reflection surface for reflecting light being emitted from the rear face of the light guiding member and having a component in the first direction, the light being reflected toward the rear face of the light guiding member as light having a component in a second direction, the second direction being an opposite direction to the first direction; and the light guiding member emits the light having the component in the first direction and the light having the component in the second direction from the front face toward the prism sheet.

In one embodiment, the reflection surface includes: a first reflection surface for reflecting the light emitted from the rear face of the light guiding member as light having a component in a direction toward the rear face of the light guiding member; and a second reflection surface for reflecting the light emitted from the rear face of the light guiding member as light having a component in the second direction.

In one embodiment, an angle between the first direction and a normal direction of each of the first reflection surface and the second reflection surface is greater than 0° and less than 90°.

In one embodiment, the reflection section is a sloped reflector or a portion of a sloped reflector; and the sloped reflector has a surface including the reflection surface.

In one embodiment, the surface of the sloped reflector is formed so as to be sawteeth-shaped.

In one embodiment, an angle between a normal direction of the rear face of the light guiding member and the first direction is greater than 0° and less than 90°.

An liquid crystal display apparatus according to the present invention comprises the above backlight unit and a liquid crystal display device having transmission apertures.

In one embodiment, a microlens array for converging light at the transmission aperture of the liquid crystal display device is further comprised.

Effects of the Invention

With a backlight unit according to the present invention, bright-dark fringes are prevented from occurring in the light emitted from the backlight unit.

Moreover, with a liquid crystal display apparatus according to the present invention, moiré fringes are prevented from occurring during displaying by the liquid crystal display apparatus, whereby good displaying can be performed.

BRIEF DESCRIPTION OF DRAWINGS

<figref idrefs="DRAWINGS">FIG. 1</figref> Diagrams for describing an embodiment of a backlight unit according to the present invention, where: (a) is a schematic cross-sectional view of the backlight unit; (b) is a schematic plan view of the backlight unit; and (c) is a schematic diagram showing the intensity of light emitted from the backlight unit.

<figref idrefs="DRAWINGS">FIG. 2</figref> A schematic cross-sectional view of a light guiding member in an embodiment of a backlight unit according to the present invention.

<figref idrefs="DRAWINGS">FIG. 3</figref> A schematic cross-sectional view of a prism sheet in an embodiment of a backlight unit according to the present invention.

<figref idrefs="DRAWINGS">FIG. 4</figref> (<i>a</i>) to (<i>d</i>) are diagrams for explaining light reflection by a sloped reflector in a backlight unit according to the present invention.

<figref idrefs="DRAWINGS">FIG. 5</figref> A schematic cross-sectional view showing an embodiment of a liquid crystal display apparatus according to the present invention.

<figref idrefs="DRAWINGS">FIG. 6</figref> A schematic diagram showing the positioning of a microlens array in an embodiment of a liquid crystal display apparatus according to the present invention.

<figref idrefs="DRAWINGS">FIG. 7</figref> A schematic cross-sectional view of another embodiment of a backlight unit according to the present invention.

<figref idrefs="DRAWINGS">FIG. 8</figref> (<i>a</i>) is a schematic cross-sectional view of a light guiding member in still another embodiment of a backlight unit according to the present invention; and (<i>b</i>) is a schematic cross-sectional view of a light guiding member in still another embodiment of a backlight unit according to the present invention.

<figref idrefs="DRAWINGS">FIG. 9</figref> (<i>a</i>) is a schematic plan view of still another embodiment of a backlight unit according to the present invention; and (<i>b</i>) is a cross-sectional view taken along line X-X′ in (a).

<figref idrefs="DRAWINGS">FIG. 10</figref> (<i>a</i>) is a schematic plan view of still another embodiment of a backlight unit according to the present invention; and (<i>b</i>) is a cross-sectional view taken along line X-X′ in (a).

<figref idrefs="DRAWINGS">FIG. 11</figref> (<i>a</i>) is a schematic plan view of still another embodiment of a backlight unit according to the present invention; and (<i>b</i>) is a cross-sectional view taken along line X-X′ in (a).

<figref idrefs="DRAWINGS">FIG. 12</figref> (<i>a</i>) is a schematic plan view of still another embodiment of a backlight unit according to the present invention; and (<i>b</i>) is a cross-sectional view taken along line X-X′ in (a).

<figref idrefs="DRAWINGS">FIG. 13</figref> (<i>a</i>) is a schematic plan view of still another embodiment of a backlight unit according to the present invention; and (<i>b</i>) is a cross-sectional view taken along line X-X′ in (a).

<figref idrefs="DRAWINGS">FIG. 14</figref> A schematic cross-sectional view of still another embodiment of a backlight unit according to the present invention.

<figref idrefs="DRAWINGS">FIG. 15</figref> A schematic cross-sectional view showing a liquid crystal display apparatus according to Comparative Example.

<figref idrefs="DRAWINGS">FIG. 16</figref> Diagrams for describing a conventional backlight unit, where: (a) is a schematic cross-sectional view of the backlight unit; and (b) is a schematic diagram showing the intensity of light emitted from the backlight unit.

<figref idrefs="DRAWINGS">FIG. 17</figref> A schematic cross-sectional view of a light guiding member in a conventional backlight unit.

<figref idrefs="DRAWINGS">FIG. 18</figref> A schematic cross-sectional view of a prism sheet in a conventional backlight unit.

<figref idrefs="DRAWINGS">FIG. 19</figref> A schematic diagram showing reflection and refraction of light in a commonly-used light guiding member.

<tables id="TABLE-US-00001" num="00001"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217pt" align="center" /><thead><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row><row><entry>DESCRIPTION OF THE REFERENCE NUMERALS</entry></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="3"><colspec colname="1" colwidth="14pt" align="left" /><colspec colname="2" colwidth="49pt" align="left" /><colspec colname="3" colwidth="154pt" align="left" /><tbody valign="top"><row><entry /><entry>100</entry><entry>liquid crystal display apparatus</entry></row><row><entry /><entry>101</entry><entry>surface light source</entry></row><row><entry /><entry>102</entry><entry>light source</entry></row><row><entry /><entry>103 </entry><entry>light guiding member</entry></row><row><entry /><entry>103a</entry><entry>principal face (front face)</entry></row><row><entry /><entry>103b</entry><entry>principal face (rear face)</entry></row><row><entry /><entry>104</entry><entry>prism sheet</entry></row><row><entry /><entry>105</entry><entry>sloped reflector</entry></row><row><entry /><entry>110</entry><entry>backlight unit</entry></row><row><entry /><entry>120</entry><entry>polarizer</entry></row><row><entry /><entry>122</entry><entry>polarizer</entry></row><row><entry /><entry>130</entry><entry>microlens array</entry></row><row><entry /><entry>140</entry><entry>liquid crystal display device</entry></row><row><entry /><entry>150</entry><entry>active matrix substrate</entry></row><row><entry /><entry>151</entry><entry>transparent glass substrate</entry></row><row><entry /><entry>152</entry><entry>reflection electrode</entry></row><row><entry /><entry>153</entry><entry>transparent electrode</entry></row><row><entry /><entry>154</entry><entry>transmission aperture</entry></row><row><entry /><entry>160</entry><entry>liquid crystal layer</entry></row><row><entry /><entry>170</entry><entry>counter substrate</entry></row><row><entry /><entry>171</entry><entry>transparent glass substrate</entry></row><row><entry /><entry>172</entry><entry>transparent electrode</entry></row><row><entry namest="1" nameend="3" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, with reference to the drawings, an embodiment of a backlight unit according to the present invention and a liquid crystal display apparatus having the backlight unit will be described. The liquid crystal display apparatus of the present embodiment is a transflective type liquid crystal display apparatus.

<figref idrefs="DRAWINGS">FIG. 1(</figref><i>a</i>) is a schematic cross-sectional view of a backlight unit <b>110</b> of the present embodiment. <figref idrefs="DRAWINGS">FIG. 1(</figref><i>b</i>) is a schematic plan view of the backlight unit <b>110</b>. <figref idrefs="DRAWINGS">FIG. 1(</figref><i>a</i>) is a cross-sectional view taken along line X-X′ in <figref idrefs="DRAWINGS">FIG. 1(</figref><i>b</i>).

As shown in <figref idrefs="DRAWINGS">FIG. 1(</figref><i>a</i>), the backlight unit <b>110</b> differs from the conventional backlight unit <b>310</b> described with reference to <figref idrefs="DRAWINGS">FIG. 16(</figref><i>a</i>) in that a sloped reflector <b>105</b> is comprised instead of the reflector <b>305</b>.

The backlight unit <b>110</b> includes: a surface light source <b>101</b> for emitting light; a prism sheet <b>104</b> for reflecting light from the surface light source <b>101</b> in the surface normal direction; and a sloped reflector <b>105</b> which is disposed on the opposite side of the surface light source <b>101</b> from the prism sheet <b>104</b>.

The surface light source <b>101</b> includes: a light source <b>102</b> for emitting light; a reflection member <b>102</b><i>a </i>provided so as to surround the light source <b>102</b>; and a light guiding member <b>103</b> for receiving light emitted from the light source <b>102</b>, and propagating the received light in a propagation direction (first direction) P. The light source <b>102</b> is a linear light source extending in a direction which is substantially orthogonal to the propagation direction P, as shown in <figref idrefs="DRAWINGS">FIG. 1(</figref><i>b</i>). The reflection member <b>102</b><i>a </i>reflects the light emitted from the light source <b>102</b> toward the light guiding member <b>103</b>, and allows the light from the light source <b>102</b> to efficiently enter the light guiding member <b>103</b>.

The light guiding member <b>103</b> includes: a principal face (front face) <b>103</b><i>a </i>opposing the prism sheet <b>104</b>; a principal face (rear face) <b>103</b><i>b </i>opposing the reflector <b>105</b>; and an end face <b>103</b><i>c </i>which connects the front face <b>103</b><i>a </i>to the rear face <b>103</b><i>b</i>. The end face <b>103</b><i>c </i>of the light guiding member <b>103</b> receives the light emitted from the light source <b>102</b>, such that the light propagates in the propagation direction P while being repetitively reflected between the front face <b>103</b><i>a </i>and the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b>, as shown in <figref idrefs="DRAWINGS">FIG. 1(</figref><i>a</i>) and <figref idrefs="DRAWINGS">FIG. 1(</figref><i>b</i>). The front face <b>103</b><i>a </i>of the light guiding member <b>103</b> is parallel to the propagation direction P. As shown in <figref idrefs="DRAWINGS">FIG. 2</figref>, the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b> includes regions which are tilted by a tilt angle α with respect to the propagation direction P, such that the angle between the normal direction of the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b> and the propagation direction P is greater than 0° and less than 90°.

<figref idrefs="DRAWINGS">FIG. 1(</figref><i>a</i>) is referred to again. The prism sheet <b>104</b> is disposed at the front face <b>103</b><i>a </i>side of the light guiding member <b>103</b>. The prism sheet <b>104</b> has a sawteeth-shaped prism surface, the prism surface having alternately-disposed first prism slopes <b>104</b><i>a </i>and second prism slopes <b>104</b><i>b</i>. The prism surface of the prism sheet <b>104</b> opposes the front face <b>103</b><i>a </i>of the light guiding member <b>103</b>. As shown in <figref idrefs="DRAWINGS">FIG. 1(</figref><i>b</i>), ridges <b>104</b><i>c </i>are formed at boundaries between the first prism slopes <b>104</b><i>a </i>and the second prism slopes <b>104</b><i>b. </i>

The sloped reflector <b>105</b> is disposed at the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b>. The surface of the sloped reflector <b>105</b> that opposes the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b> is a reflection surface <b>105</b><i>a</i>, the reflection surface <b>105</b><i>a </i>having alternately-disposed first reflection surfaces <b>105</b><i>b </i>and second reflection surfaces <b>105</b><i>c</i>. The first reflection surfaces <b>105</b><i>b </i>and the second reflection surfaces <b>105</b><i>c </i>are each tilted with respect to the propagation direction P; that is, the angle between the normal direction of each the first reflection surfaces <b>105</b><i>b </i>and the second reflection surfaces <b>105</b><i>c </i>and the propagation direction P is greater than 0° and less than 90°. The reflection surface <b>105</b><i>a </i>is formed so as to be sawteeth-shaped. On the reflection surface <b>105</b><i>a </i>of the sloped reflector <b>105</b>, a dielectric reflection film, a metallic reflection film or the like is formed, for example.

Light from the light source <b>102</b> enters the light guiding member <b>103</b>, and propagates inside the light guiding member <b>103</b> in the propagation direction P. As has been described above with reference to <figref idrefs="DRAWINGS">FIG. 19</figref>, inside the light guiding member <b>103</b>, when light enters an interface between the front face <b>103</b><i>a </i>of the light guiding member <b>103</b> and the air at an incident angle which is smaller than a predetermined incident angle (angle of total reflection), a portion of the light is refracted at the interface between the front face <b>103</b><i>a </i>and the air so as to be emitted forward, and a portion of the light is reflected at the interface between the front face <b>103</b><i>a </i>and the air. On the other hand, when light enters the interface between front face <b>103</b><i>a </i>of the light guiding member <b>103</b> and the air at an incident angle which is equal to or greater than the angle of total reflection, the light is totally reflected.

The light which is emitted forward from the front face <b>103</b><i>a </i>of the light guiding member <b>103</b> will be designated as light L<b>1</b>. The light L<b>1</b> has a component which is in the propagation direction P and in the direction from the light guiding member <b>103</b> toward the prism sheet <b>104</b>. The light L<b>1</b> having been emitted forward enters into the prism sheet <b>104</b>, and is reflected by the second prism slopes <b>104</b><i>b </i>of the prism sheet <b>104</b> so as to be emitted off the prism sheet <b>104</b> in the surface normal direction.

On the other hand, the light which has been reflected at the interface between the front face <b>103</b><i>a </i>of the light guiding member <b>103</b> and the air travels toward the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b>, and the light which is refracted at the interface between the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b> and the air is emitted rearward from the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b>. The light which is emitted rearward from the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b> will be designated as light L<b>2</b>. The light L<b>2</b> has a component which is in the propagation direction P and in the direction from the light guiding member <b>103</b> toward the sloped reflector <b>105</b>. Once reflected by the second reflection surface <b>105</b><i>c </i>of the sloped reflector <b>105</b>, the light L<b>2</b> becomes light L<b>2</b>′ having a component in the opposite direction to the propagation direction P. In the following descriptions of the present specification, the opposite direction to the propagation direction P may be referred to as a second direction. The light L<b>2</b>′ having been reflected by the second reflection surface <b>105</b><i>c </i>of the sloped reflector <b>105</b> enters the light guiding member <b>103</b>, and propagates within the light guiding member <b>103</b> in the second direction. Finally, from the front face <b>103</b><i>a</i>, the light guiding member <b>103</b> emits forward the light L<b>2</b>′ having a component which is in the second direction and in the direction from the light guiding member <b>103</b> toward the prism sheet <b>104</b>. The light L<b>2</b>′ having been emitted forward enters into the prism sheet <b>104</b>, and is reflected by the first prism slopes <b>104</b><i>a </i>of the prism sheet <b>104</b>, so as to be emitted from the prism sheet <b>104</b> in the surface normal direction.

Thus, in the prism sheet <b>104</b>, the first prism slopes <b>104</b><i>a </i>reflect the light L<b>2</b>′ in the surface normal direction, whereas the second prism slopes <b>104</b><i>b </i>reflect the light L<b>1</b> in the surface normal direction. Therefore, in accordance with the backlight unit <b>110</b> of the present embodiment, the intensity of the light which is reflected by the second prism slopes <b>104</b><i>b </i>is substantially the same as the intensity of the light which is reflected by the first prism slopes <b>104</b><i>a. </i>

<figref idrefs="DRAWINGS">FIG. 1(</figref><i>c</i>) is a schematic diagram showing the intensity of the light emitted from the backlight unit <b>110</b> of the present embodiment. In <figref idrefs="DRAWINGS">FIG. 1(</figref><i>c</i>), out of the light emitted from the backlight unit <b>110</b>, the intensity of the light reflected by the first prism slope <b>104</b><i>a </i>of the prism sheet <b>104</b> corresponds to reference numeral C, whereas the intensity of the light reflected by the second prism slope <b>104</b><i>b </i>of the prism sheet <b>104</b> corresponds to reference numeral D. In the backlight unit <b>110</b>, the light traveling via the sloped reflector <b>105</b> is reflected by the first prism slopes <b>104</b><i>a </i>of the prism sheet <b>104</b>, whereas the light not traveling via the sloped reflector <b>105</b> is reflected by the second prism slopes <b>104</b><i>b </i>of the prism sheet <b>104</b>. As a result, the difference between the intensity of the light ascribable to the second prism slopes <b>104</b><i>b </i>(corresponding to reference numeral D) and the intensity of the light ascribable to the first prism slopes <b>104</b><i>a </i>(corresponding to reference numeral C) is smaller than the difference in light intensity in the conventional backlight unit <b>310</b> having been described with reference to the <figref idrefs="DRAWINGS">FIG. 16(</figref><i>b</i>). Preferably, there is no difference in light intensity in the backlight unit <b>110</b> of the present embodiment. Thus, hardly any bright-dark fringes corresponding to the pitch of the prism sheet <b>104</b> occur in the light which is emitted from the prism sheet <b>104</b>, and preferably uniform light is emitted from the prism sheet <b>104</b>.

In the backlight unit <b>110</b>, the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b> includes regions which are tilted by the tilt angle α with respect to the propagation direction P, as shown in <figref idrefs="DRAWINGS">FIG. 2</figref>. Herein, the tilt angle α is non-zero. In this case, even if the incident angle of the light which enters the interface between the front face <b>103</b><i>a </i>of the light guiding member <b>103</b> and the air is greater than the angle of total reflection so that this light is totally reflected, it is reflected, after the total reflection, by the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b>. As a result, the incident angle of the light which again enters the front face <b>103</b><i>a </i>of the light guiding member <b>103</b> becomes smaller than the angle of total reflection, so that a portion of the light is emitted from the front face <b>103</b><i>a </i>of the light guiding member <b>103</b>. The tilt angle α of the rear face <b>103</b><i>b </i>is 120, for example.

As shown in <figref idrefs="DRAWINGS">FIG. 3</figref>, in the prism sheet <b>104</b> of the backlight unit <b>110</b>, each vertex angle between a first prism slope <b>104</b><i>a </i>and a second prism slope <b>104</b><i>b </i>is θ. The vertex angle θ of the prism sheet <b>104</b> is 62°, for example, and the pitch of the prism sheet <b>104</b> is 30 μm, for example. The ridges <b>104</b><i>c </i>are formed at the boundaries between the first prism slopes <b>104</b><i>a </i>and the second prism slopes <b>104</b><i>b</i>, and as shown in <figref idrefs="DRAWINGS">FIG. 1(</figref><i>b</i>), the direction in which the ridges <b>104</b><i>c </i>extend intersects the propagation direction P of light, and is preferably orthogonal thereto.

Moreover, as shown in <figref idrefs="DRAWINGS">FIG. 4(</figref><i>a</i>), each triangle in the sawteeth-shaped cross section of the sloped reflector <b>105</b> has a vertex angle φ<b>1</b>, a base angle φ<b>2</b>, and a base angle φ<b>3</b>, where φ<b>1</b>+φ<b>2</b>+φ<b>3</b>=180°. The base angle φ<b>2</b> is an angle which is more toward the light source <b>102</b> than is the base angle φ<b>3</b>.

As shown in <figref idrefs="DRAWINGS">FIG. 4(</figref><i>b</i>), the angles of the vertex angle φ<b>1</b>, the base angle φ<b>2</b>, and the base angle φ<b>3</b> are prescribed so that the principal ray of the light L<b>2</b> strikes each second reflection surface <b>105</b><i>c </i>of the sloped reflector <b>105</b> at an incident angle of substantially 0°. As a result, the area of the first reflection surface <b>105</b><i>b </i>provided between the vertex angle φ<b>1</b> and the base angle φ<b>3</b> is greater than the area of the second reflection surface <b>105</b><i>c </i>provided between the vertex angle φ<b>1</b> and the base angle φ<b>2</b>, the base angle φ<b>2</b> being greater than the base angle φ<b>3</b>.

Moreover, even in the case where the light L<b>2</b> strikes a second reflection surface <b>105</b><i>c </i>of the sloped reflector <b>105</b> at an incident angle other than 0°, as shown in <figref idrefs="DRAWINGS">FIG. 4(</figref><i>c</i>), the light L<b>2</b> is reflected by the second reflection surface <b>105</b><i>c</i>, thus becoming light having a component in the second direction, and then is reflected by a first reflection surface <b>105</b><i>b</i>, thus becoming light having a component in the direction toward the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b>. The light L<b>2</b>′ having been reflected by the first reflection surface <b>105</b><i>b </i>again enters the light guiding member <b>103</b>. Alternatively, as shown in <figref idrefs="DRAWINGS">FIG. 4(</figref><i>d</i>), the light L<b>2</b> is reflected by a first reflection surface <b>105</b><i>b</i>, thus becoming light having a component in the direction toward the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b>, and then is reflected by a second reflection surface <b>105</b><i>c</i>, thus becoming light L<b>2</b>′ having a component in the second direction. The light L<b>2</b>′ having been reflected by the second reflection surface <b>105</b><i>c </i>again enters the light guiding member <b>103</b>.

Thus, also through a plurality of times of reflection, the reflection surface <b>105</b><i>a </i>of the sloped reflector <b>105</b> converts the light having a component in the first direction and in the direction toward the sloped reflector <b>105</b> into light having a component in the direction toward the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b> and in the second direction.

The vertex angle φ<b>1</b>, the base angle φ<b>2</b>, and the base angle φ<b>3</b> of the sloped reflector <b>105</b> are such that: the vertex angle φ<b>1</b>=88°; the base angle φ<b>2</b>=78°; and the base angle φ<b>3</b>=14°, for example. However, these angles are only exemplary. In the case where the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b> has a tilt angle α of 12°, they may be in the ranges such that φ<b>1</b>≧84°; φ<b>2</b>≧72°; and 14°≦φ<b>3</b>≦22°. In general, it is preferable that the vertex angle φ<b>1</b>, the base angle φ<b>2</b>, and the base angle φ<b>3</b> respectively satisfy φ<b>1</b>≧72°+α, φ<b>2</b>≧84°−α, and 14°≦φ<b>3</b>≦22°.

The pitch of the light guiding member <b>103</b> may differ depending on the size of the light guiding member <b>103</b>. However, in order to ensure uniform luminance of the light emitted from the front face <b>103</b><i>a </i>of the light guiding member <b>103</b>, the pitch of the light guiding member <b>103</b> is made relatively long at the end face <b>103</b><i>c </i>where the light is received, and the pitch of the light guiding member <b>103</b> becomes shorter away from the end face <b>103</b><i>c</i>. For example, in a 5-cm light guiding member <b>103</b>, the pitch of the light guiding member <b>103</b> varies from 200 μm to 10 μm. The pitch of the prism sheet <b>104</b> is from 10 μm to 50 μm, for example, and the pitch of the sloped reflector <b>105</b> is in the range from 30 μm to 200 μm. Note that the pitches of the light guiding member <b>103</b>, the prism sheet <b>104</b>, and the sloped reflector <b>105</b> are mainly determined based on ease of production.

Each of the first reflection surfaces <b>105</b><i>b </i>and the second reflection surfaces <b>105</b><i>c </i>is a rectangular face extending in a direction which is substantially parallel to the direction in which the ridges <b>104</b><i>c </i>of the prism sheet <b>104</b> extend.

<figref idrefs="DRAWINGS">FIG. 5</figref> is a schematic cross-sectional view of a liquid crystal display apparatus <b>100</b> according to the present embodiment. The liquid crystal display apparatus <b>100</b> of the present embodiment is a transflective type liquid crystal display apparatus having the backlight unit <b>110</b>.

The liquid crystal display apparatus <b>100</b> includes the backlight unit <b>110</b>, a pair of polarizers <b>120</b> and <b>122</b>, a microlens array <b>130</b>, and a liquid crystal display device <b>140</b>. The microlens array <b>130</b> is interposed between the backlight unit <b>110</b> and the liquid crystal display device <b>140</b>, whereas the polarizer <b>120</b> is interposed between the backlight unit <b>110</b> and the microlens array <b>130</b>. Moreover, the liquid crystal display device <b>140</b> is interposed between the microlens array <b>130</b> and the polarizer <b>122</b>.

The liquid crystal display device <b>140</b> has a screen size of 2.4 inches diagonal (vertical: 49.0 mm, horizontal: 36.7 mm). The pixels, or the minimum displaying units of the liquid crystal display device <b>140</b>, are disposed in a stripe array of 240 horizontal pixels (R,G,B)×320 vertical pixels. The pixel pitches are 0.153 mm along the vertical direction, and 0.051 mm along the horizontal direction.

The liquid crystal display device <b>140</b> includes an active matrix substrate <b>150</b>, a counter substrate <b>170</b>, and a liquid crystal layer <b>160</b> interposed between the active matrix substrate <b>150</b> and the counter substrate <b>170</b>. The liquid crystal layer <b>160</b> is sealed between the active matrix substrate <b>150</b> and the counter substrate <b>170</b>, and includes liquid crystal molecules having a positive anisotropy of dielectric constant, for example.

The active matrix substrate <b>150</b> includes a transparent glass substrate <b>151</b>, reflection electrodes <b>152</b> provided on the transparent glass substrate <b>151</b>, and a transparent electrode <b>153</b> provided on the transparent glass substrate <b>151</b>. Transmission apertures <b>154</b> are provided in the portions of the active matrix substrate <b>150</b> where the reflection electrodes <b>152</b> are not provided. A driving circuit (not shown) for supplying voltages for changing the orientation states of the liquid crystal molecules is connected to the transparent electrode <b>153</b>. As the driving circuit drives the transparent electrode <b>153</b>, the orientations of the liquid crystal molecules are controlled, whereby the intensity of the light which is transmitted through the liquid crystal layer <b>160</b> is controlled. Moreover, a plurality of thin film transistors (not shown) are provided in a matrix shape on the active matrix substrate <b>150</b>, each thin film transistor controlling the charges of the reflection electrodes <b>152</b> and the transparent electrode <b>153</b>. Moreover, the transparent glass substrate <b>151</b> has the microlens array <b>130</b> provided thereon.

The microlens array <b>130</b> includes a plurality of spherical lenses having a curvature of 80 μm. The spherical lenses are formed by applying a transparent acrylic or epoxy-type resin having a refractive index of 1.51 on the transparent glass substrate <b>151</b>, and then processing it into a pattern. As shown in <figref idrefs="DRAWINGS">FIG. 6</figref>, the spherical lenses are disposed in a general delta array. The pitches of the spherical lenses are 76.5 μm along the propagation direction in which the light is propagated in the light guiding member <b>103</b> of the backlight unit <b>110</b>, and 51 μm along a direction lying orthogonal to the propagation direction and in the plane of the light guiding member <b>103</b>.

<figref idrefs="DRAWINGS">FIG. 5</figref> is referred to again. The counter substrate <b>170</b> includes a transparent glass substrate <b>171</b> and a transparent electrode <b>172</b> which is formed on the transparent glass substrate <b>171</b>.

Each transmission aperture <b>154</b> defined by the transparent electrode <b>153</b> has a circular shape with a diameter of 0.042 mm, and the transmission apertures <b>154</b> are disposed so as to correspond to the centers of the spherical lenses of the microlens array <b>130</b> shown in <figref idrefs="DRAWINGS">FIG. 6</figref>.

Moreover, the thickness of the active matrix substrate <b>150</b> is adjusted so that the distance from each transmission aperture <b>154</b> to the apex of each spherical lens of the microlens array <b>130</b> is 220 μm.

In the liquid crystal display apparatus <b>100</b> of the present embodiment, light having hardly any bright-dark fringes occurring therein enters the microlens array <b>130</b>, so that the liquid crystal display apparatus <b>100</b> can perform displaying without causing moiré fringes.

Hereinafter, a comparison will be made between the liquid crystal display apparatus according to the present invention and a liquid crystal display apparatus according to Comparative Example.

<figref idrefs="DRAWINGS">FIG. 15</figref> is a schematic cross-sectional view of a liquid crystal display apparatus <b>200</b> according to Comparative Example. The liquid crystal display apparatus <b>200</b> differs from the liquid crystal display apparatus <b>100</b> shown in <figref idrefs="DRAWINGS">FIG. 5</figref> in that the reflector <b>205</b> has a rectangular cross section.

A backlight unit <b>210</b> of the liquid crystal display apparatus <b>200</b> has a construction similar to that of the backlight unit <b>310</b> described with reference to <figref idrefs="DRAWINGS">FIG. 16(</figref><i>a</i>), and the reflector <b>205</b> of the backlight unit <b>210</b> has a rectangular solid shape.

The optical characteristics of the liquid crystal display apparatus of the present embodiment and the liquid crystal display apparatus of Comparative Example are shown in Table 1. As shown in Table 1, in accordance with the liquid crystal display apparatus of the present embodiment, moiré fringes can be prevented while maintaining substantially the same luminance as the luminance of the liquid crystal display apparatus of Comparative Example.

<tables id="TABLE-US-00002" num="00002"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="3"><colspec colname="offset" colwidth="84pt" align="left" /><colspec colname="1" colwidth="70pt" align="center" /><colspec colname="2" colwidth="63pt" align="center" /><thead><row><entry /><entry namest="offset" nameend="2" rowsep="1">TABLE 1</entry></row><row><entry /><entry namest="offset" nameend="2" align="center" rowsep="1" /></row><row><entry /><entry>Luminance</entry><entry>Moiré Fringes</entry></row><row><entry /><entry namest="offset" nameend="2" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="4"><colspec colname="offset" colwidth="14pt" align="left" /><colspec colname="1" colwidth="70pt" align="left" /><colspec colname="2" colwidth="70pt" align="char" char="." /><colspec colname="3" colwidth="63pt" align="center" /><tbody valign="top"><row><entry /><entry>Comparative Example</entry><entry>100</entry><entry>YES</entry></row><row><entry /><entry>Present Embodiment</entry><entry>95</entry><entry>NO</entry></row><row><entry /><entry namest="offset" nameend="3" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

Thus, in accordance with the backlight unit <b>110</b> of the present embodiment, both the first prism slopes <b>104</b><i>a </i>and the second prism slopes <b>104</b><i>b </i>of the prism sheet <b>104</b> contribute to emission of light in the surface normal direction, whereby bright-dark fringes can be prevented. Since bright-dark fringes which would cause moiré do not occur, the liquid crystal display apparatus <b>100</b> can adequately perform displaying.

Note that, in the liquid crystal display apparatus <b>200</b> of Comparative Example, moiré fringes could be eliminated by broadening the interspace between the prism sheet <b>204</b> and the microlens array <b>230</b>. However, broadening the interspace between the prism sheet <b>204</b> and the microlens array <b>230</b> is not preferable because the thickness of the liquid crystal display apparatus <b>200</b> would become thicker than practical thicknesses.

Note that the backlight unit according to the present invention is not limited to the backlight unit which been described with reference to <figref idrefs="DRAWINGS">FIG. 1</figref> to <figref idrefs="DRAWINGS">FIG. 4</figref>.

In another embodiment of the backlight unit <b>110</b> according to the present invention, as shown in <figref idrefs="DRAWINGS">FIG. 7</figref>, the reflection surface <b>105</b><i>a </i>of the reflector <b>105</b> is not tilted with respect to the propagation direction P. Specifically, the normal direction of the first reflection surfaces <b>105</b><i>b </i>of the reflector <b>105</b> is perpendicular to the propagation direction P, whereas the normal direction of the second reflection surfaces <b>105</b><i>c </i>of the reflector <b>105</b> is parallel to the propagation direction P.

In this case, too, as has been described with reference to <figref idrefs="DRAWINGS">FIG. 4(</figref><i>c</i>) and <figref idrefs="DRAWINGS">FIG. 4(</figref><i>d</i>), light which strikes the reflector <b>105</b> is reflected by the first reflection surfaces <b>105</b><i>b </i>to become light having a component in the direction toward the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b>, and is reflected by the second reflection surfaces <b>105</b><i>c </i>to become light having a component in the second direction.

Note that the cross-sectional shape of the light guiding member <b>103</b> is not limited to the shape shown in <figref idrefs="DRAWINGS">FIG. 1(</figref><i>a</i>) and <figref idrefs="DRAWINGS">FIG. 7</figref>. In still another embodiment of the backlight unit according to the present invention, the light guiding member <b>103</b> has a substantially wedge-shaped cross section, as shown in <figref idrefs="DRAWINGS">FIG. 8(</figref><i>a</i>). Generally speaking, there is a tendency that the intensity of the light emitted from the front face <b>103</b><i>a </i>of the light guiding member <b>103</b> becomes greater toward the light source <b>102</b>. When the light guiding member <b>103</b> has a wedge-shaped cross section, the intensity of the light emitted from the front face <b>103</b><i>a </i>of the light guiding member <b>103</b> can be made uniform.

In still another embodiment of the backlight unit according to the present invention, as shown in <figref idrefs="DRAWINGS">FIG. 8(</figref><i>b</i>), the light guiding member <b>103</b> is a substantially rectangular solid, such that the light guiding member <b>103</b> has a rectangular cross section. In this case, the angle between the normal direction of the rear face <b>103</b><i>b </i>of the light guiding member <b>103</b> and the propagation direction is 90°.

Note that, although the light source <b>102</b> for emitting light for the light guiding member <b>103</b> is a linear light source in the backlight unit <b>110</b> which has been described with reference to <figref idrefs="DRAWINGS">FIG. 1(</figref><i>b</i>), the light source <b>102</b> in the backlight unit <b>110</b> according to the present invention is not limited thereto.

In still another embodiment of the backlight unit <b>110</b> according to the present invention, as shown in <figref idrefs="DRAWINGS">FIG. 9(</figref><i>a</i>) and <figref idrefs="DRAWINGS">FIG. 9(</figref><i>b</i>), the light source <b>102</b> has a point light source <b>102</b><i>c </i>and a linear light guiding member <b>102</b><i>d</i>. In this case, light emitted from the point light source <b>102</b><i>c </i>enters the linear light guiding member <b>102</b><i>d</i>, and light from the linear light guiding member <b>102</b><i>d </i>enters the light guiding member <b>103</b>.

In still another embodiment of the backlight unit <b>110</b> according to the present invention, as shown in <figref idrefs="DRAWINGS">FIG. 10(</figref><i>a</i>) and <figref idrefs="DRAWINGS">FIG. 10(</figref><i>b</i>), the light source is a plurality of point light sources <b>102</b><i>c. </i>

In still another embodiment of the backlight unit <b>110</b> according to the present invention, as shown in <figref idrefs="DRAWINGS">FIG. 11(</figref><i>a</i>) and <figref idrefs="DRAWINGS">FIG. 11(</figref><i>b</i>), one corner of the light guiding member <b>103</b> is beveled, and the point light source <b>102</b><i>c </i>is disposed near the beveled portion of the light guiding member <b>103</b>. The point light source <b>102</b><i>c </i>is oriented diagonally from the beveled portion of the light guiding member <b>103</b>, so that the light guiding member <b>103</b> propagates light from the point light source <b>102</b><i>c </i>in a propagation direction P. The direction in which the ridges <b>104</b><i>c </i>of the prism sheet <b>104</b> extend intersects the propagation direction P, and is preferably substantially orthogonal thereto. Each of the first reflection surfaces <b>105</b><i>b </i>and the second reflection surfaces <b>105</b><i>c </i>of the sloped reflector <b>105</b> is a rectangular face which is substantially parallel to the direction in which the ridges <b>104</b><i>c </i>of the prism sheet <b>104</b> extend.

In still another embodiment of the backlight unit <b>110</b> according to the present invention, as shown in <figref idrefs="DRAWINGS">FIG. 12(</figref><i>a</i>) and <figref idrefs="DRAWINGS">FIG. 12(</figref><i>b</i>), a plurality of point light sources <b>102</b><i>c </i>are provided. The light guiding member <b>103</b> is beveled at one corner, and the plurality of point light sources <b>102</b><i>c </i>are disposed near the beveled portion of the light guiding member <b>103</b>. As a whole, the plurality of point light sources <b>102</b><i>c </i>are oriented diagonally from the beveled portion of the light guiding member <b>103</b>, so that the light guiding member <b>103</b> propagates light from the plurality of point light sources <b>102</b><i>c </i>in a propagation direction P. Again, the direction in which ridges <b>104</b><i>c </i>of the prism sheet <b>104</b> extend intersects the propagation direction P, and is preferably substantially orthogonal thereto. Moreover, each of the first reflection surfaces <b>105</b><i>b </i>and the second reflection surfaces <b>105</b><i>c </i>of the sloped reflector <b>105</b> is a rectangular face which is substantially parallel to the direction in which the ridges <b>104</b><i>c </i>of the prism sheet <b>104</b> extend.

Although light enters from one side of the light guiding member <b>103</b> in the above descriptions, the present invention is not limited thereto.

In still another embodiment of the backlight unit <b>110</b> according to the present invention, as shown in <figref idrefs="DRAWINGS">FIG. 13(</figref><i>a</i>), two light sources <b>102</b> and <b>102</b><i>e</i>, each of which is a linear light source, are disposed on both side faces of a light guiding member <b>103</b>. Herein, as shown in <figref idrefs="DRAWINGS">FIG. 13(</figref><i>b</i>), a reflection surface <b>105</b><i>a </i>of a sloped reflector <b>105</b> is formed symmetrically so that a base angle φ<b>2</b> and a base angle φ<b>3</b> are equal, and the light guiding member <b>103</b> is also formed symmetrically.

If the propagation direction of the light from the light source <b>102</b> were to be conveniently referred to as a first propagation direction and the propagation direction of the light from the light source <b>102</b><i>e </i>a second propagation direction, then the second propagation direction would be the opposite direction to the first propagation direction. If the intensity of the light emitted from the light source <b>102</b> is the same as the intensity of the light emitted from the light source <b>102</b><i>e</i>, the intensity of the light having a component in the first propagation direction, out of the light emitted from the light guiding member <b>103</b> toward the prism sheet <b>104</b>, is the same as the intensity of the light having a component in the second propagation direction. Alternatively, the light source <b>102</b> may be formed so as to surround the perimeter of the light guiding member <b>103</b>.

In still another embodiment of the backlight unit according to the present invention, as shown in <figref idrefs="DRAWINGS">FIG. 14</figref>, the sloped reflector <b>105</b> includes a plurality of reflection sections <b>105</b><i>d </i>and a substrate <b>105</b><i>e </i>on which the plurality of reflection sections <b>105</b><i>d </i>are provided. Each reflection section <b>105</b><i>d </i>has first reflection surfaces <b>105</b><i>b </i>and second reflection surfaces <b>105</b><i>c</i>, such that the alternately-disposed first reflection surfaces <b>105</b><i>b </i>and second reflection surfaces <b>105</b><i>c </i>form a reflection surface <b>105</b><i>a</i>. As the substrate <b>105</b><i>e</i>, any arbitrary substrate that is capable of affixing the reflection sections <b>105</b><i>d </i>can be used.

The sloped reflector <b>105</b> is formed in the following manner. A resin layer is formed on the substrate <b>105</b><i>e</i>, and slopes having a sawteeth cross section are formed on the resin layer. The slopes of the resin layer are formed by using a photolithography technique or a transfer technique. On the surface of the resin layer, a metallic reflection film having a high light reflectance, e.g., aluminum or silver, or a dielectric reflection film in which thin dielectric films having different refractive indices are alternately stacked is deposited, thus forming the oblique reflection section <b>105</b><i>c </i>having the reflection surface <b>105</b><i>a. </i>

Note that, a plurality of reflection sections <b>105</b><i>d </i>are provided in the backlight unit <b>110</b> shown in <figref idrefs="DRAWINGS">FIG. 14</figref>, there may only be one reflection section <b>105</b><i>d</i>. Moreover, the reflection sections <b>105</b><i>d </i>do not need to be provided on the substrate <b>105</b><i>e. </i>

Although the transflective type liquid crystal display apparatus <b>100</b> having the backlight unit <b>110</b> was illustrated in the above descriptions, the present invention is not limited thereto. The backlight unit <b>110</b> according to the present invention may be used in a transmission type liquid crystal display apparatus.

INDUSTRIAL APPLICABILITY

With a liquid crystal display apparatus having the backlight unit according to the present invention, moiré fringes due to bright-dark fringes can be prevented. Therefore, the liquid crystal display apparatus can be suitably used for mobile phones, mobile terminals, word processors, office automation (OA) devices such as laptop-type personal computers, various video devices, game devices, television receivers, and the like.